Biological specimens such as blood, sperm, ova, embryos, nucleotide strands and enzymes, multi cellular specimens such as skin, and the like, are conventionally stored in racks or trays which are placed in a cryogenically cooled chamber either manually or robotically. The specimens or samples are themselves placed in ampules or vials which are then placed on the racks or trays that are immersed in the cryogenic liquid or vapor. The ampules and/or vials are typically provided with color coded dosures that can be manually coded by using an ink marker or bar coded so as to identify the contents of the ampules or vials.
U.S. Pat. No. 4,377,077 describes a cryo-unit which includes a refrigerant unit in which specimens or samples to be cryo-preserved are placed, which refrigerant unit is then stored in another refrigerator.
U.S. Pat. No. 5,233,844 describes an automated cryo-unit which has a large number of moving parts. The components of this cryo-unit are particularly prone to failure at cooling temperatures due to the generation of thermoelastic stresses which result from differential thermal contraction during cool down from ambient temperatures to operating temperatures. This unit also suffers from the formation of water ice due to the lack of a vacuum seal in the cryochamber. This unit utilizes liquid cryogens and thus its operating lifetime is limited by the supply of those cryogens. While it is understood that these cryogens are to be replenished, a catastrophic failure mechanism nonetheless exists whereby the samples would be inadvertently warmed up should the supply of these cryogens be interrupted. Since this unit uses liquid nitrogen as its cryogen, its base temperature is limited to −196° C.
U.S. Pat. No. 4,969,336 discloses a cryo-unit which also has a large number of moving parts and uses liquid cryogens to reach its operating temperatures. The operating temperatures and reliability of storage are thus limited by these liquid cryogens.
U.S. Pat. No. 5,921,102 discloses a cryo-unit which uses a liquid cryogen wherein the specimen samples are placed in the liquid cryogen or its vapors during storage. The cryogen used is typically nitrogen. This unit thus can result in undesirable cross contamination between the samples and the cryogen. The use of liquid cryogens also limits the storage temperatures and the storage reliability of the specimen samples.
U.S. Pat. No. 6,467,285 discloses an automated storage and retrieval apparatus for low temperature freezers that are used to preserve specimen samples. Liquid carbon dioxide or liquid nitrogen is used as a cryogen to obtain these temperatures. Specimens to be stored are robotically inserted into a chamber in the freezer where the humidity is reduced to guard against the occurrence of frost, and then the specimens are moved into a storage chamber in the freezer. The specimens are robotically placed on a carousel in the storage chamber. The specimen holders are bar coded so that they can be retrieved and properly identified. The storage temperatures of the freezer are limited by the use of a liquid cryogen to obtain operating temperatures. This patent does not suggest any way to achieve freezer operating temperatures in the range of −140° C. to −196° C. which it states are desirable. In fact its operating temperatures are between −50° C. and −90° C. Also, the immersion of the specimen samples in liquid cryogens raises the possibility that the specimen samples will become cross contaminated by the cryogen.
It is noted that all of the above-noted cryogenic freezers have operating temperatures that are limited by the immersion of the samples in liquid nitrogen.
Because molecular processes slow down at lower temperatures, it would be desirable to provide a cryogenic storage assembly which can achieve operating temperatures that are colder than those that can be achieved with the immersion of the samples in liquid nitrogen. It would also be desirable to preserve the specimen samples in a vacuum so as to reduce sample crystallization and contamination.